1. Field of the Invention
The present invention relates to a suspension apparatus for auto-focus lens device and a method for fabricating the same, more particularly an apparatus used in camera which provides the functions of suspension and support by forming a lens holder and a supporting base respectively at either end of a suspension spring in one piece by means of plastic injection molding.
2. Description of the Prior Art
A standard camera 1 comprises a lens set 11, a sensor 12 and a focusing mechanism (not shown in the figure). The lens set 11 forms an image on sensor 12 by refracting the light rays from an object (as shown in FIG. 1). If the distance between lens set 11 and sensor 12 (back focal length, BFL) is fixed, the lens can only show clearly objects at a specific distance (e.g. the hyperfocal distance of 2–3 meters away). For the camera to shoot objects at a close distance, the distance between lens set 11 and sensor 12 must be adjusted using a focusing and zooming mechanism.
The focusing and zooming mechanism 2 used in conventional camera (as shown in FIG. 2) typically includes an expensive precision drive element 21 (e.g. stepping motor, ultrasonic motor, and piezoelectric actuator) to supply the power needed to drive the lens holder 22 that carries the lens set 11 and a large number of driving elements. Such design has the deficiencies of complicated mechanical configuration, time-consuming assembly, bulkiness and high cost. Most seriously, it consumes a large amount of power. As technology advances, camera makers have been gearing their efforts towards developing high picture quality and small-sized products for easy carriage. Other electronic device makers also focus on integrating more functions in one device by, for example, combining the functions of photographing and mobile communication of handset, the functions of photographing and personal digital assistant (PDA), or the functions of photographing and notebook computer to give the device more powerful video functions. Based on the design of a common power supply having the same capacity as that for a device with single function, how to reduce the size and the cost of product, how to lower power consumption to effectively improve the standby time and run time of the integrated product become the focus of research for electronic product manufacturers.
In conventional focusing and zooming lens structure, an elastic element is often used to provide the functions of cushion, positioning and repositioning. A conventional lens unit 3 as shown in FIG. 3 comprises a lens mount 31 and a lens frame 32. The lens mount 31 has lens 311 at the top, a hollow space 312 in the middle, and an electromagnetic coil set 33 wound around its periphery at the bottom. The lens frame 32 is arranged in the space 312 of lens mount 31 and able to slide up and down the space 312. The lens frame 32 has two protruding members (not shown in figure) and the shape of space 312 complements that of lens frame 32 so that lens frame 32 will not turn in space 312 when sliding. The lens frame 32 is made of magnetically conductive metal material so that the magnetic force generated after the electromagnetic coil set 33 are charged can attract the lens frame 32 to displace downward. The lens frame 32 is disposed with a lens 321 therein. The upper part and lower part of space 312 in lens mount 31 has respectively an upper stop member 313 and a lower stop member 314 with lens frame 32 situated therebetween and a spring 34 disposed between the lens frame 32 and lower stop member 314. By such structural design, the lens frame 32 in the lens unit 3 can be pushed against the upper stop member 313 by the thrust from the spring 34. At the time of focus adjustment, electric current is passed through electromagnetic coil set 33 to generate magnetic force that can attract the metallic lens frame 32 to displace downward and achieve the objective of focus adjustment.
In the conventional lens unit structure just described, the spring 34 used is bulky, hence taking considerable space. On the other hand, in coordination with the use of spring 34, an upper stop member 313 and a lower stop member 314 must be disposed in the upper and lower sections of space 312 in lens mount 31, rendering the whole structure more complicated. Conventional lens unit assembles the lens mount 31, lens frame 32 and spring 34 one by one after they are separately fabricated. The whole assembly process is not only tedious and time consuming, the unavoidable inaccuracy in assembly also adds to the burden of quality control operation.